The video of civilians suffering from the effects of chemical weapons - believed to be chlorine and sarin - is undoubtedly real, but a local doctor told Mr Fisk they were suffering from hypoxia - oxygen loss - and dust inhalation.

"On this night, there was wind and huge dust clouds began to come into the basements and cellars where people lived," said Assim Rahaibani. "People began to arrive here suffering from hypoxia, oxygen loss."

The confusion began when someone shouted "gas!" and panic broke out.

"People started throwing water over each other. Yes, the video was filmed here, it is genuine, but what you see are people suffering from hypoxia - not gas poisoning."

Dr Rahaibani wasn't there when it happened - the doctors were reportedly giving evidence at a chemical weapons inquiry in Damascus.

France has claimed it has proof chemical weapons were used in the attack, but adds it's "likely that proof and essential elements are disappearing from this site" as independent observers have been prevented from going in.

The World Health Organisation said last week hundreds of people were treated for exposure to "toxic chemicals", including "severe irritation of mucous membranes, respiratory failure and disruption to central nervous systems".

Mr Fisk says he had free rein to wander the city, and people told him "armed Islamist groups" make up the gas attack claims. Dr Rahaibani twice called rebel gunmen "terrorists", suggesting he may be aligned with the Assad regime.

Mr Fisk, who speaks fluent Arabic, has covered the Middle East for decades. While he's won several awards for his work, UK newspaper The Times reports a number of his more damning reports which paint the West in a bad light haven't always been backed up with evidence.